The most constant thing about beaches is that they are always in flux

Analyzing how beaches change, and may change in the future, is no easy task. To make accurate predictions, researchers need data on a complicated array of forces and factors

The most constant thing about beaches is that they are always in flux. Wind, waves, and currents move sand around, building up shorelines in some places and eroding them elsewhere, with consequences for coastal wildlife, including birds. Analyzing how beaches change, and may change in the future, is no easy task. To make accurate predictions, researchers need data on a complicated array of forces and factors, from big-picture elements like topography and tides to the tiniest components of a coast: grains of sand.

But until recently, sand has been relatively understudied. Enter SandSnap—a collaborative project sponsored by the U.S. Army Corps of Engineers, James Madison University, and consultancy Marda Science LLC. Since 2022, the project has enlisted community scientists to build a database of beach sand across the United States, from both freshwater sites like the Great Lakes and ocean beaches. The information will support beach restoration projects, including habitat for at-risk shorebirds like Red Knots and terns

The SandSnap database currently contains some 2,800 analyzed images of beach sand, along with their latitude, longitude, and a measure of grain size—a crucial factor in how beaches change over time. The process is simple: Participants go to a debris-free section of dry sandy beach, place any coin on the sand for scale, snap a photo with a cell phone, and upload the image to the project's web site. Analysts measure the sand’s grain size using a deep-learning neural network trained on a range of sediment samples from diverse locations. Slightly more than 70 percent of the existing images are from U.S. beaches; the rest are from sites worldwide.

Sand comes in many sizes and shapes, reflecting the rocks and shells that produced it and the geologic processes that wore them down. “Beaches exist in a rough equilibrium between the size of the waves and the size of the sand-grains,” says David Young, an Army research engineer. The larger sand-grains are, the more energy it takes to move them, so the presence of finer sands and clays indicates that a beach has small, gentle waves. If bigger sand-grains start washing up, wave action is likely increasing. To build an accurate computer model of a shifting coastline, scientists need to know the exact size of the beach’s sand-grains. But no comprehensive database of sand-grain sizes in North America exists, and collecting this information would be prohibitively expensive for any single agency or laboratory, especially because the composition of beach sand changes over time. Since beaches are popular destinations, community scientists are well positioned to help fill the knowledge gaps.

Though the Corps is best known for dredging rivers, harbors, and channels to keep ship traffic moving nationwide, the agency also restores or creates tens of thousands of acres of wetlands every year, sometimes using dredged sand to do so. “The Corps used to dump a lot of valuable dredged sediments offshore, but they’ve become better partner in reusing some of it,” says Brad Winn, vice president for resilient habitats at Manomet Conservation Sciences. Currently, the agency reuses about 30 to 35 percent of the material it dredges from waterways for so-called “beneficial purposes,” such as habitat restoration, and aims to increase that figure to 70 percent by 2030.

But to meet that goal, federal engineers need more information about sand sizes and types at specific locations. Dredged material can’t be dumped randomly on the shore. “The sand needs to match the sand on the beach in size and color,” Young says. If the sand size and composition doesn’t match what’s already present, dredged material can wash away or change the profile of the beach—and that could harm shorebird species that rely on the habitat to nest or to feed during migration. Intertidal shoals, zones exposed at low tide and underwater at high tide, are “a grocery store for species like plovers, oystercatchers and migratory sandpipers,” Winn says. Foraging shorebirds pluck invertebrates from wet sands and small fish from tidal pools. On dry beaches, birds find insects and marine organisms trapped in seaweed at the wrack line.

In recent years the Corps has used dredged sand and mud to restore or create bird habitat in locations around the country, from Cape May County, New Jersey, to Hampton Roads, Virginia, and Savannah, Georgia. Environmentalists would like to see this work expand. “Sea level rise, erosion of dry sand beaches, and loss of intertidal areas are serious threats to beach-nesting and migratory birds,” Winn says.

For anyone inspired to submit images, Brian McFall, an Army coastal engineer, offers some tips. Your photograph should capture an area slightly larger than a business card, with the coin in the corner. “Make sure you can see the sand-grains in your image, and that they aren’t blurry,” McFall says. SandSnap data has already been included in a few